The retired CBS host was in the audience of Steve Martin and Edie Brickell’s new musical, “Bright Star,” where “Grey’s Anatomy” actress Kate Burton was seated directly across the aisle.

“When Letterman went over to say hi during intermission, he startled Burton, who clearly didn’t recognize Dave under all that facial hair,” said a spy. “She nearly jumped out of her seat! But once she heard his voice, she put [two and two] together and was very friendly.”